A device of this type is commercially available and is used for photobiological purposes, for example, as a facial irradiator for direct pigmentation of the human skin (tanning without erythema) or in phototherapy of dermatological diseases. In this case the body is exposed to long-wave ultraviolet radiation (UV-A radiation) for some time. A relatively small high-pressure metal halide lamp emitting radiation at a wavelength of between about 300 and 400 nm is preferably used as a radiation source in the known device. The glass filter plate positioned in front of the exit side of the reflector passes only UV-A radiation (315-400 nm) whereas UV-B radiation (280-315 nm) originating from the radiation source is obstructed by the plate.
A problem of such known device is that UV-B radiation originating from the radiation source may also emanate if the glass filter plate breaks. This is undesirable, because such radiation may be harmful to the human body.